Rejuvenated through a merger: Beryllium abundance in the ancient star HD 65907

Abstract

The chemistry, kinematics, and low Li abundance of the star HD 65907 suggest that despite its isochronal age of ∼5 Gyr, it is a merger of two old Pop. II stars. To further investigate this star, we determine its Li and Be abundances and evaluate its radial velocity time series and activity cycle. Li and Be abundances were determined via spectral synthesis of their resonance lines using HARPS and UVES spectra. HARPS data were also used to study variations in the star’s radial velocity and activity levels. Our analysis reveals that HD 65908 is severely Li- and Be-depleted. Its radial velocity is nearly constant, with a small modulation likely associated with stellar activity, which points to the lack of an undetected close companion. These results are strong pieces of evidence in favor of the stellar merger scenario.